Speech synthesis system



G. L. CLAPPER SEARCH @0516 SPEECH SYNTHESIS SYSTEM Filed Dec. 21. 1961 9 Sheets-Sheet 1 -11-) WORDCODE STORAGE V INDICATOR GENERATOR MATRIX PANEL V GATE OSCILLATORS Bl 7 03 I I0? I08 52 osc. B3 LOUD B4 SPEAKER READOUT DRWER MATRIX B5 osc.

.08 TIME DURATION CONTROL 1 k H M 1 I l O L 01 DURATION DECODE H8 READOUT RING R W I V 1-1 1 11 1 PG ||4 ON '26 OFF Q8 A V (20) .1111. A

2 1 L" PG ||9\ j V A --|l5 INT. W so) RESET 125 J G 1 A INT. RING DRIVE pg |2| I .4 (2401 SAMPLE l INTEGRATORS 1 H5 H7 PULSE GEN. PULSE k GENERATORS 7 V Y j DIFFERENTIATE DIFFERENTSATOR MIX ISM I CHANGE PULSE (cP') INVENTOR Gnung L. Clapper ORNEYS Aug. 27, 1963 CLAPPER 3,102,165

SPEECH SYNTHESIS SYSTEM 'Fi.ied Dec. 21. 1901 9 Sheets-Sheet 2 +0 v. 204 205 FIG. 2. g

AMPLITUDE 0 CONTROL CURRENT OUTPUT (MIX) FIG. 20.

042404400 VALUES my BAND FREQUENCY 042. CAP. CAP. CAP. CAP. 0. P. s. 204 2 205 200 201 200 200 Aug. 27, 1963 G. .L. CLAPPER 3,102,165

SPEECH SYNTHESIS SYSTEM Filed Dec. 21. 1961 9 Sheets-Sheet 3 FIG.3.

FROM READOUT RING Aug. 27, 1963 G. L. CLAPPER 3,102,165

SPEECH SYNTHESIS SYSTEM, V

Filed Dec. 21. 1961 9 Sheets-Sheet 4 Aug. 27, 1963 ca. L. CLAPPER SPEECH SYNTHESIS SYSTEM 9 Sheets-Sheet 5 Filed Dec. 21. 1961 FIG.6.

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G. L. CLAPPER SPEECH SYNTHESIS SYSTEM Filed Dec. 21. 1961 9 Sheets-Sheet 8 T0 DURATION DECODE United States Patent 3,102,165 SPEECH SYNTHESIS SYSTEM Genung L. Clapper, Vestal, N.Y., assignor to International Business Machines Corporation, New York, N .Y., a corporation of New York Filed Dec. 21, 1961, Ser. No. 160,995 6 Claims. (Cl. 179-1) This invention relates to speech synthesis systems and more particularly to a system for reconstructing audible speech from digital codes.

Many systems have been developed for coding speech in digital form and for reconstructing audible speech from the digital codes. One of the major problems in such systems is to provide for the coding and reconstruction of speech with the smallest possible number of information bits, that is, provide the most'efficient coding.

Another problem present in speech synthesis systems which reconstruct audible speech from digital codes is reconstructing the sounds in a smooth and continuous manner. Many prior art speech coding and synthesis systems generate digital codes at periodic sampling intervals and reconstruct the speech from these digital codes at the periodic intervals. Often the sample intervals are in the middle of a speech sound and the result is a discontinuity in the produced speech. These systems utilizing sampling techniques are also wasteful of information bits since a single sound is often specified by a plurality of codes when a number of sampling times occur during the sound. It would be more desirable to have the single sound specified by a single code.

Another problem in speech synthesis systems is the mixing of the outputs of oscillators in a manner which achieves natural sound effects. Many prior art systems have utilized constantly running oscillators and have gated the outputs of these oscillators to a mixer to synthesize the speech sound. In such systems the sharp turn on and turn off of the oscillators produces unnatural clicking sounds in the outputs.

These and other problems are solved by the speech synthesis system of the subject disclosure. Accordingly, it is an object of this invention to provide an improved speech synthesis system which reconstructs speech from an efficient usage of digital codes by analyzing a time duration code for each of the reconstructed sounds instead of relying on codes at periodic sampling intervals.

It is another object of the present invention to provide a speech synthesis system which produces natural sounds in a continuous manner with no discontinuities in the middle of a reproduced sound.

It is a further object of the present invention to provide oscillators for a speech synthesis system, the outputs of which are miXed to produce sounds which have a natural beginning and-termination and so produce speech in a more natural manner.

In accordance with one embodiment of the invention audible sounds are reproduced from digital codes containing six bits specifying the frequencies present in the sound and two bits specifying the time duration of the sound. Each of the six frequency bits gates an associated oscillator. The outputs of the oscillators are mixed and drive a loud speaker which produces the audible sounds. The two time duration bits specify four different time durations for the sound. The two time duration bits are decoded and a second gate of the specified time duration is generated. This second gate is integrated to produce a sloping leading edge and is used to gate on the oscillators. The integration of the second gate obviates the sharp leading edge and results in the oscillators being gated on in a gradual manner to produce a natural sound output.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings in which:

FIGURE 1 is a block diagram of the speech synthesis system;

FIGURE 2 is a circuit diagram of the gate and oscillator;

FIGURE 2a is a table showing the capacitor values for various representative output frequencies of the gated oscillators;

FIGURE 3 is a circuit diagram of the loud speaker and driver;

FIGURE 4 is a circuit diagram of the readout matrix;

FIGURE 5 is a circuit diagram of the readout ring;

FIGURE 6 is a circuit diagram of the duration decode drivers;

FIGURE 7 is a circuit diagram of the duration decoder;

FIGURE 7a is a table showing the changes in the circuitry of FIGURE 7 required to adapt the circuit to produce the other time duration gates;

FIGURE 8 is a circuit diagram of the change pulse generator;

FIGURE 9 is a circuit diagram of the bi-polar differentiator;

FIGURE 10a shows the start input to diiferentiator 122;

FIGURE 10b shows the output of the change pulse generator 123;

FIGURE shows the sample pulse from the sample pulse generator 127;

FIGURE 10d shows the D7 bit;

FIGURE 10c shows the complement of the D7 bit;

FIGURE 10 shows the D8 bit;

FIGURE 10g shows the complement of the D8 bit;

FIGURE 10h shows the output of pulse generator 114;

FIGURE 10: shows the output of pulse generator 115;

FIGURE 10 shows the output of pulse generator 116;

FIGURE 10k shows the output of pulse generator 117;

FIGURE l0l shows the combined outputs of the inte- .grators;

FIGURE 10m shows the B1 bit;

FIGURE l0n shows the B2 bit;

FIGURE 100 shows the B3 bit;

FIGURE 10p shows the B4 bit;

FIGURE 10: shows the B5 bit;

FIGURE 10r shows the B6 bit;

FIGURE 10s shows the output of ring driver 125.

In referring to the drawings, the first digit of each reference numeral denotes the drawing on which the component is found. For example, the readout matrix is shown in FIGURE 1 and the diode 434 is shown in FIGURE 4. In describing the logic of the various circuits, two-state signals will be referred to as being up or down. The signal is up when in its more positive state and down when in its more negative state.

Over-A ll System Referring to FIGURE 1 there is shown a microphone 101 and a Word code generator 102 for generating digital codes representative of speech sounds. The word code generator forms no part of this invention. A suitable word code generator is shown in the co-pending application Serial No. 161,089, filed December 21, 1961, entitled Word Code Generator, to the present inventor and assigned to the assignee of the present application. The code generated is a compact 8 bit code for each discrete sound in an audio word. Six bits contain information concerning the frequency content of the sound and two bits define the time duration of the sound element. This code is digital in nature and readily adaptable to storage in punch cards, magnetic cores or any other storage medium. A storage medium 103, which may be any one of the types just mentioned, is shown diagrammatically in FIGURE 1 together with an indicator panel 104 for displaying the stored codes.

A readout matrix 105 is provided to transfer words from storage 103 to the speech synthesizer. The readout matrix makes the eight bits of each digital code available at the output. The bits B1-B6 are the frequency bits and each bit controls an associated gated oscillator. The gated oscillators are shown diagrammatically at 106. The outputs of all oscillators are mixed together and drive the output driver 107, which, in turn, drives the loud speaker 108.

The bits D7 and D8 specify the time duration of the sound. Drivers 109 produce the complements of D7 and D8 and the D7 and D8 bits in a form suitable for decoding. The D7 and D8 bits specify one of four time durations which in the present embodiment have been chosen as milliseconds, 60 milliseconds, 120 milliseconds and 240 milliseconds. AND gates 110-113 decode the time duration and enable either the 20 millisecond pulse generator 114, the 60 millisecond pulse generator 115, the 120 millisecond pulse generator 116 or the 240 millisecond pulse generator 117. Each of these pulse generators produces a gate having the specified time duration. The output of each pulse generator is integrated in one of the integrators 118-121 in order to smooth out the sharp leading edge. The integrated gate turns on the gated oscillators in a smooth manner.

In order to continuously transfer new codes to the synthesizer, means are provided to detect the end of each gate from the pulse generators 114-117 and to change the code present at the output of the readout matrix in response thereto. To do this, the end of the time dunation gate is differentiated in ditferentiator and mixer 122, the output of which drives a sample pulse generator 123, which produces a 15 millisecond change pulse. The beginning of the change pulse is detected by a bi-polar differentiator 124 which drives the ring driver 125. The beginning of the change pulse calls for a new code element by advancing the readout ring 126. The end of the change pulse is also detected by bi-polar differentiator 124 which drives the sample pulse generator 127 in response thereto. The sample pulse generator 127 produces a pulse which samples AND gates 110-113 to set up a new time duration waveform for the oscillator. The oscillators 106 are again gated on by certain ones of the B1-B6 lines and by the output of one of the integrators 118-121. The oscillator output is a complex waveform containing the frequency elements called for in the digital code and lasting for a time duration specified by the D7 and D8 bits of the code.

The circuits shown in block form in FIGURE 1 will now be described in greater detail in conjunction with the remaining drawings.

Gated Oscillators The circuitry for each of the gated oscillators 106 is shown in FIGURE 2. An oscillator of the type shown in FIGURE 2 is provided for each of the frequencies to be reproduced in the speech synthesis system. The outputs of all oscillators are mixed by a current summing technique to produce a composite waveform. This allows the generation of vowel sounds in speech synthesis. Prior art speech synthesis systems have utilized constantly running oscillators and have gated and mixed the outputs of these oscillators. The oscillators of the subject system, however, are normally off and are gated on with a controllable build-up and fall-01f of the amplitude which allows natural effects to be achieved.

The gate input from readout matrix 105 is applied through resistor 201 to the base of transistor 202. When the input gate goes from the negative to a more positive level, the oscillator is enabled. The oscillator produces oscillations having a gradually increasing amplitude which is controlled by the amplitude control waveform. This waveform, produced by integrators 118-121, is applied through resistor 203 to the base of transistor 202. The oscillator itself includes transistor 202, transistor 203a and a panallel-T filter in a degenerative feedback loop. The degenerative feedback loop includes capacitors 204, 205, 206, 207, 208 and 209. The values of these capacitors determine the frequency of oscillation of the oscillator.

The table shown in FIGURE 2a gives the values of capacitors 204-209 for various representative output frequencies. It will be understood, of course, that the frequencies shown are merely representative and any desired frequency can be obtained by changing the values of capacitors 204-209.

Loud Speaker Driver Readout Matrix Details of the readout matrix are shown in FIG- URE 4. The matrix includes eighty diode AND gates; only the four corner AND gates are shown in FIGURE 4, but the operation of the readout matrix will be readily apparent from the description of these four elements. The matrix includes ten vertical columns of AND gates, each column including eight AND gates for each of the eight bits in a particular digital code. It is assumed that the storage medium 103 stores ten digital codes at a time. Hence the readout matrix contains ten vertical columns corresponding to each of these ten digital codes. Each bit of each digital code is connected to the \anode of one diode. For example, each of the eight bits of one digital code is connected to the anode of diodes 401-408 (only diodes 401 and 408 being shown). Similarly, the eight bits of one of the other ten digital codes from storage matrix 103 are connected to bits 409-416 (only diodes 409 and 416 being shown). The logic elements are driven from the readout ring. The first stage of the readout ring is connected to the anodes of diodes 417-424 (only diodes 417 and 424 being shown). Similarly, the other stages of the ring are connected to corresponding diodes in each of the AND gates. The tenth stage of the readout ring 126 is connected to the anodes of diodes 425- 433. The output of each logic element is from a diode corresponding to the diodes 434, 435, 436 or 437 which are shown. The anodes of these diodes in the top horizontal row are connected to the base of output driver 438. Diodes in other horizontal rows are connected to similar drivers; the anodes of diodes 435 and 437 are connected to the base of output driver 439. The output from readout matrix 105 is from the collectors of these transistors. For example, the D8 bit of each code is present on line 440 from the collector of transistor 439.

The operation of the readout matrix is as follows. When the first stage of the readout ring 126 is set, the line 441 is down and the voltage at the anode of diodes 434 or 435 will be up or down depending upon the inputs from the storage matrix to the diodes 401-408. If the line from the storage matrix 103 to the anode of diode 401 is down, then the anode of diode 434 will be down, the transistor 438 will be turned on and the collector of transistor 438 will be up thus indicating the presence of a B1 bit in the code presently being decoded. Similarly, up conditions of the lines B1-B7 and D7 and D8 indicate the presence of that bit in the code being decoded. As the readout ring 126 advances to subsequent stages, the remaining diode logic elements in the readout matrix will decode the codes in storage matrix 103 and indicate the presence or absence of bits in the output lines.

Readout Ring The circuitry of readout ring 126 is shown in FIGURE 5. Readout ring 126 comprises a reset stage including transistors 501 and 502 and ten readout stages. The first stage, including transistors 503 and 504, is shown and the tenth stage, including transistors 505 and 506, is shown. Initially, the manual reset switch 507 is depressed to set the ring to the reset stage. Depression of this switch removes ground potential from the emitters of transistors 503 and 505, thus cutting these transistors 011 and also cutting otf all transistors corresponding to transistors 504 and 506 because of the collector to base coupling between 503 and 504 and between 505 and 506. Depression of switch 507 also applies ground potential to one end of the resistor 508 and causes a positive pulse to be coupled to the emitter of transistor 501 and to the base of transistor 502. Transistor 502 turns on, a negative going pulse is coupled from the collector of transistor 502 to the base of transistor 501, thus turning that transistor on and latching transistor 502 to the conducting condition by reason of the connection from the collector of 501 to the base of 502. Positive ring drive pulses are applied over line 509 to the anodes of diodes 510, 511 and 512. The first ring drive pulse passes through diode 510 to the base of transistor 501 thereby turning that transistor 01f. As transistor 501 turns off the base of transistor 502 goes negative and transistor 502 cuts off. The action is regenerative and transistors 501 and 502 are out off. But as transistor 502 cuts off a positive pulse is coupled through capacitor 513 to the base of transistor 504 tending to turn that transistor on. As this transistor turns on, a negative going voltage is applied to the base of transistor 503 tending to turn that transistor on. The action is regenerative and transistors 503 and 504 become conducting. When transistor 504 conducting, a negative voltage, or down condition, is applied to the line 514. This line is connected to the line 441 in the readout matrix shown in FIGURE 4. When transistors 503 and 504 are in the conducting state, thereby applying negative potential to line 514, the digital code bits connected to the anodes of diodes 401 and 408 are read out of the storage matrix. The next ring drive pulse is coupled through diode 511 to turn transistors 503 and 504 off and to turn the second stage of the readout ring on. Succeeding ring drive pulses turn succeeding stages of the readout ring on thereby reading out successive digital codes from the readout matrix.

Duration Decode Drivers The duration decode drivers 109 are shown in detail in FIGURE 6. The D7 bit from the readout matrix 105 is connected to the base of transistor 601. Transistor 601 is an emitter follower and produces an output on line 602 indicative of the D7 bit. The emitter of transistor 601 is also connected to the base of inverter 604 which produces an output on line 605 indicative of the complement of the D7 bit.

The D8 bit is connected to the base of transistor 606. The D8 bit is obtained from the line 440 in FIGURE 4. Transistor 606 is an emitter follower and transistor 607 is an inverter and produce the D8 bit and the complement of the D8 bit respectively.

Duration Decoder The details of the AND gates 110-113, the pulse generators 114-117 and the integrators 118-121 are shown in FIGURE 7. The circuitry shown is the circuitry for AND gate 110, pulse shaper 114 and integrator 118. However, it will be readily apparent that the circuitry for the other AND gates, pulse \shapers, and integrators is quite similar.

The complements of the D7 and D8 bits, taken from the collectors of transistors 604 and 607 respectively, are connected to the cathodes of diodes 701 and 702. These diodes, together with diode 703, form an AND gate for the D7 and D8 complements and the sample pulse from the sample pulse generator 127. When all three of these signals are up, the voltage at the anode of diode 704 is up. The positive voltage is coupled through diode 704 to trigger the pulse shaper. This pulse shaper includes the norm-ally non-conducting transistor 705 and the nor mally conducting transistor 706. The positive pulse at the base of transistor 705 causes that transistor to conduct. A negative pulse is coupled through the capacitor 707 to cut off the transistor 706. The transistors 705 and 706 will remain in their unstable conducting conditions for a time period determined by the value of capacitor 707. In the instant embodiment, the pulse generator 114 is to generate a pulse 20 milliseconds long. In this eX- ample, a value of capacitor 707 of 1.5 microfarads will produce such :a time duration pulse. This 20 millisecond duration pulse is connected to the integrator including the transistor 708 and the capacitor 709. The output of this integrator is connected to the gated oscillaors 106 to gate the oscillators on. The collector of transistor 706 is also connected to the difierentiators and mixers 122 which detect the trailing edge of the time duration gate in order to initiate the ring drive and sample pulses.

FIGURE 7a is a table showing the changes in the circuitry of FIGURE 7 in order to adapt the circuit to produce the other time duration gates. For example, the 60 millisecond time duration pulse generator 115 has a capacitor 707 with a value of 5.0 microfarads. The D7 bit and the complement of the D8 bit are connected to the diodes 70-1 and 702 respectively and the capacitor 709 has a value of 0:1 'microfarad. Table 7a lists the changes necessary to adapt the circuit for the pulse shapers 116 and 117 also.

Change Pulse Generator The details of differentiator and mixer 122 and pulse stretcher 123, which produce the change pulse, are shown in FIGURE 8. The time duration gate from the collector of transistor 706 is connected through the coupling capacitor '801 to the base of transistor 802. The time duration gate has a positive going leading edge which does not afiect the transistor 802 since the base is clamped at ground potential by the diode 803. However, the negative going trailing edge of the time duration gate is coupled through the NP junction of transistor 802 to the collector of the normally conducting transistor 804 and, through capacitor 807 to the base of normally non-conducting transistor 805. The normally non-conducting transistor 805 is turned on and the normally conducting transistor 804 is turned off. A change pulse is thereby generated on the output line 806. The time duration of this change pulse depends on the value of capacitor 807 and the setting of the variable resistor 808. The out-puts of pulse generators 115-117 are coupled through capacitors 809-811, respectively. A start key 812 is provided to couple l3. negative going pulse through capacitor 813 to manually start the system initially.

Bi-Polar Diflerentiator The details of the bi-polar difierentiator 124 are shown in FIGURE 9. The 'bi-polar d-ifierentiator detects the beginning of the change pulse to produce a pulse to drive the readout ring 126 and detects the trailing edge of the change pulse to produce a sample pulse to sample AND gates -113. The transistor 901 is normally cut off as a result of current flowing through forward biased diodes 902 and 903. Since the drop in the diodes is substantially equal, points 904 and 905 are normally at 0.2 volt and +0.2 volt, respectively. The mid-point of diodes 906 and 907 is therefore near ground potential. With the input terminal at -l2 volts the input capacitor is charged to 12 volts. A positive input transient drives the junction of diodes 906 and 907 to about +7.5 volts. Current then flows through diode 907, the emitter base diode of transistor 901, and the resistor 908 to ground. The transistor conducts current through the collector to the output which rises sharply to ground and then follows the emitter to about +6.5 volts. As the transient current ceases to flow, the transistor 901 cuts off and the output returns to the 12 bolt level. The positive transient applied to the base of normally conducting transistor 909 is sufficient to cut that transistor off and the normally nonconducting transistor 910 is rendered conducting. Transistors 909 and 910 remain in their astable states for a time suificient to generate a ring drive pulse which is ap plied to the readout ring 126. The pulse present on the line 911 is connected to the ring drive line 509 in FIG- URE 5.

When the change pulse goes negative at the trailing edge, the negative going transient is coupled through diode 906 and transistor 9.12 to switch the conducting states of normally conducting transistor 913 and normally non-conducting transistor 914. Transistors 913 and 914 remain in their astable states for a time period sufficient to generate the sample pulse on output line 915. Output line 915 is connected to the AND gates 110-113 to sample the states of the time duration bits D7 and D8.

Operation of Speech Synthesis System The operation of the speech synthesis system can best be explained in conjunction with the waveforms of FIG- URE 10. These waveforms depict the operation of the speech synthesizer in reconstructing the word LIGHT. The word LIGHT is made up of seven discrete portions. These are: (l) UH, (2) LL, (3) AH, (4) EE, (5) UH, (6) STOP, (7) T. The operation of the synthesizer in reconstructing each of these seven discrete sounds can be shown in the waveforms.

FIGURE a shows the manual start pulse applied to differentiator 122. As shown in FIGURE 10b this results in the generation of a change pulse from the pulse shaper .123. The leading edge of the change pulse is from the pulse shaper 123. The leading edge of the change pulse is differentiated by bi-polar differentiator 124 and this results in ring drive circuit 125 producing the ring drive pulse shown in FIGURE 10s. The ring is advanced to the next position and the next stored digital code is read out of readout matrix 105. This code includes the Bl-B6 bits as shown in FIGURES lOm-lOr and the D7 and D8 bits shown in FIGURES 10d and 102. These bits specify, by the presence of the B6 bit, that the 220 c.p.s. frequency is present in the sound UH. The D7 and D8 bits specify that the sound will be 60 milliseconds long.

The trailing edge of the first change pulse, shown in FIGURE 10b, is also differentiated by bi-polar difierentiator 124 which drives the sample pulse generator 127 to produce the sample pulse shown in FIGURE 10c. This pulse samples AND gates 110-113 in order to decode the D7 and D8 bits. Because the D7 bit is up and the complement of the D8 bit is up, only AND gate 111 will pass the sample pulse and this results in enabling pulse generator 115. Pulse generator 115 produces a 60 millisecond gate as shown in FIGURE 10i. This is integrated in integrator 119, the output of which is shown in FIGURE 101. The waveform of FIGURE 10l is connected to the amplitude control input of the gated oscillators. Since only the B6 bit is present, only the 220 c.p.s. oscillator will be gated on. The oscillator will be gated on in a gradual manner by the waveform of FIG- URE 101. As the integrated waveform of FIGURE 10l slopes back to the off condition, the 220 c.p.s. oscillator is gated off again and the sound UH has been produced. When the 60 millisecond gate, FIGURE 10i, goes off, the differentiator mixer 122 produces a pulse which again triggers pulse shaper 123 and produces the second change pulse shown in FIGURE 10b. The operation of the speech synthesizer in producing the sound LL is similar to that described above in producing the sound UH. The remainder of the sounds are similarly produced. Note that the sixth discrete sound is a STOP containing no audible frequencies.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiment, it will be understood that various omissions, substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A speech synthesizer for reproducing a sound from a digital code, said digital code including bits specifying the frequencies present in said sound and bits specifying the time duration of said sound, said system comprising a plurality of gated oscillators, each of said gated oscillators producing an output of a different one of the frequencies present in said sound, an audio transducer, the outputs of said oscillators being connected to drive said audio transducer, each of said oscillators producing an output in response to the presence of two gating inputs to the oscillator, a readout matrix specifying the frequencies present in said sound and the time duration of said sound, one gating input to each of said oscillators being connected to said readout matrix whereby a particular oscillator is enabled when said digital code contains a bit specifying that frequency, means for decoding said time duration bits, means responsive to said last named decoding means for generating a gate of the specified time duration, said last named gate being connected to the second gating input of all of said oscillators.

2. The system recited in claim 1 wherein said means for decoding said time duration bits includes a plurality of AND gates, said time duration bits being selectively connected to said AND gates whereby only one AND gate produces an output for a particular combination of said time duration bits, and wherein said means for generating a gate of the specified time duration includes a plurality of pulse generators, each of said pulse generators producing a gate of different, specified, time duration, each of said AND gates being connected to enable an associated one of said pulse generators, the outputs of said pulse generators being connected to the second gating input of all oscillators.

3. The system recited in claim 2 and a plurality of integrators, the output of each of said pulse generators being connected to an associated one of said integrators, each of said integrators producing a gate having a sloping leading edge and a sloping trailing edge, the outputs of said integrators being connected to the second gating inputs of each of said gated oscillators whereby said gated oscillators are turned on and off in a gradual manner.

4. A speech synthesizer for reproducing a sound from a digital code, said digital code including bits specifying the frequencies present in said sound and bits specifying the time duration of said sound, said system comprising a readout matrix, a readout ring, said readout ring being connected to said readout matrix whereby said readout matrix reads out successive digital codes as said readout ring steps through its stages, a plurality of gated oscillators, each of said oscillators producing an output of a diiferent one of the frequencies present in said sound, an audio transducer, the outputs of said oscillators driving said audio transducer, each of said oscillators producing an output in response to the presence of two gating inputs to the oscillator, said readout matrix being connected to one gating input to each of said oscillators so that the frequency specifying bits of said digital codes enable particular oscillators when the frequencies generated by that oscillator are specified by said digital code, means for decoding said time duration bits, said time duration bits from said readout matrix being connected to said last named means, means responsive to said decoding means for generating a gate of the specified time duration, said last named gate being connected to the second input of all of said oscillators, a ditferentiator, said time duration gate being connected to said dilferentiator, said diflerentiator producing an output upon the occurrence of the trailing edge of said time duration gate, a change pulse generator, the output of said ditferentiator being connected to enable said change pulse generator, a bi-polar difierentiator, the output of said change pulse generator being connected to said bi-polar diiferentiator, said bi-polar difierentiator producing a first output upon the occurrence of the leading edge of said change pulse and a second output upon the occurrence of the trailing edge of said change pulse, said first output being connected to said readout ring so that said readout ring is advanced one stage upon the occurrence of said first output, said second output being connected to said means for decoding said time duration bits whereby said decoding means produces an output upon the occurrence of the second output of said bi-polar differentiator.

5. The system recited in claim 4 wherein said means for decoding said time duration bits includes a plurality of AND gates, said time duration bits being selectively connected to said AND gates whereby only one AND gate produces an output for a particular combination of said time duration bits, and wherein said means for generating a gate of the specified time duration includes a plurality of pulse generators, each of said pulse generators producing a gate of a difierent, specified, time duration, each of said AND gates being connected to enable an associated one of said pulse generators, the outputs of said pulse generators being connected to the second gating input of all oscillators.

6. The system recited in claim 5 and a plurality of integrators, the output of each of said pulse generators being connected to an associated one of said integrators, each of said integrators producing a gate having a sloping leading edge and a sloping trailing edge, the outputs of said integrators being connected to the second gating inputs of each of said gated oscillators whereby said gated oscillators are turned on and off in a gradual manner.

No references cited. 

1. A SPEED SYNTHESIZER FOR REPRODUCING A SOUND FROM A DIGITAL CODE, SAID DIGITAL CODE INCLUDING BITS SPECIFYING THE FREQUENCIES PRESENT IN SAID SOUND AND BITS SPECIFYING THE TIME DURATION OF SAID SOUND, SAID SYSTEM COMPRISING A PLURALITY OF GATED OSCILLATORS, EACH OF SAID GATED OSCILLATORS PRODUCING AN OUTPUT OF A DIFFERENT ONE OF THE FREQUENCIES PRESENT IN SAID SOUND, AN AUDIO TRANSDUCER, THE OUTPUTS OF SAID OSCILLATORS BEING CONNECTED TO DRIVE SAID AUDIO TRANSDUCER, EACH OF SAID OSCILLATORS PRODUCING AN OUTPUT IN RESPONSE TO THE PRESENCE OF TWO GATING INPUTS TO THE OSCILLATOR, A READOUT MATRIX SPECIFYING THE FREQUENCIES PRESENT IN SAID SOUND AND THE TIME DURATION OF SAID SOUND, ONE GATING INPUT TO EACH OF SAID OSCILLATORS BEING CONNECTED TO SAID READOUT MATRIX WHEREBY A PARTICULAR OSCILLATOR IS ENABLED WHEN SAID DIGITAL CODE CONTAINS A BIT SPECIFYING THAT FREQUENCY, MEANS FOR DECODING SAID TIME DURATION BITS, MEANS RESPONSIVE TO SAID LAST NAMED DECODING MEANS FOR GENERATING A GATE OF THE 